Signal producing means



Oct. 17, 1939. v R J w sE 2,176,442

SIGNAL PRODUCING MEANS Filed Dec. 31, 1935 lNVEN TOR R.J. WIS E wzmvmATT R N EY Patented Oct. 17, 1939 PATENT OFFICE SIGNAL PRODUCING MEANSRaleigh J. Wise, Dunellen, N. J., assignor to The Western UnionTelegraph Company, New York, N. Y., a corporation of New YorkApplication December 31, 1935, Serial No. 57,019

1 Claim.

The present invention relates to optical signal producing arrangementsand more particularly to novel arrangements for reversing the effect oflight incident upon a photosensitive device to 5, permit reception of apositive record from a positive representation of a picture or message.

The primary object of this invention is to provide a transmittingarrangement employing photoelectric cells in a novel manner whereby thelight values of successive elements of a scanned field acting on one ofthe photosensitive devices serve to produce a signal output suitable forreproduction'of a positive image.

Optical transmitting arrangements employing two photocells as disclosedin the prior art for producing an inverted picture modulated output donot provide for independent adjustment of the amount of light incidenton each cell to com pensate for unavoidable diiferences in the cells.Accordingly, another object of the present invention is to provide anovel arrangement employing two photocells to enable reception of apositive record from a positive representation of an image to betransmitted and for independent regulation of the light incident on eachphotocell.

Still another object of the present invention resides in the provisionof coupling means employed in a novel manner between a photoelectricscanning device and a circuit in communication with a receiving device.

Other and more specific objects of the invention will appear from thefollowing detailed description of two illustrative embodiments:

Fig. 1 is a diagrammatic illustration of a photoelectric pickup systemembodying the invention in its preferred form; and

Fig. 2 is a view similar to Fig. 1 illustrating a modification.

The optical pickup arrangement of the present invention is particularlyadapted for facsimile picture or message transmission when a positiverecord is desired and therefore the invention will be described asapplied to this use. Referring to Fig. l of the drawing, the subjectmatter to be scanned may conveniently be mounted upon a drum 5 which isrotated through a suitable driving connection 6 by a motor 1. Means 8are provided for advancing the message drum axially as it rotates sothat the entire field will be covered by the scanning beam of light.Light from a suitable source 9 is concentrated by the lens ll upon thesurface to be scanned and is reflected into the photosensitive devicel2, the latter being suitably supported in a housing or the like (notshown) at a proper distance from the outer periphery of the cylinder 5.The light source 9 is preferably of adjustable intensity and therheostat I0 provides a simple means for securing adjustment of the lightintensity; however, any means giving an equivalent result may be used.The spot of light projected upon the surface of the cylinder 5 by thelens I I is caused to traverse the cylinder in a longitudinal directionas the cylinder rotates by reason of the axial movement of the cylinder,the means 8 determining the extent of movement of the cylinder duringeach rotation. In this manner the spot of light will follow a helicalpath as the cylinder 5 is rotated, thus producing a scanning action.

The foregoing method of obtaining a scanning movement per se is wellknown, as are various other methods of scanning a given field, and it isto be understood that any of the known methods of scanning may beemployed in practicing the invention.

The light which is incident upon the photocell, is interrupted by ashutter or light chopper M which may be a disc as illustrated, having aseries of equally spaced openings or notches l5 adjacent its outer edge.Where the reflected beam is to be interrupted, a lens l6 serves to bringthe reflected light beam to a focus substantially in the plane of thedisc l4 so that it may pass through the openings l5 in succession. Thedisc I4 is secured upon a rotatable shaft l8 which is driven in anysuitable manner either from the motor I or a separate source ofmechanical power. The number of holes in the disc and the speed ofrotation of the shaft may vary within wide limits, depending upon thedesired rate of scanning, the constants of the communication circuitemployed between stations, and other factors. The output appearingacross the terminal of the photocell I2 is of such a character as tocause reproduction of a negative record in the usual receiver employedin facsimile systems. As stated above, the present invention isconcerned with providing a pickup system furnishing an output suitable.for the reproduction of positive record and this purpose is effioientlyaccomplished by employing a second photocell 2| connected in parallelwith the cell I2.

A second source of light 22 adjustable in intensity as by the rheostat23 is provided to illuminate the photocell 2 I. A lens 24 correspondingin function to the lens l6 serves to bring the light beam from thesource to a focus substantially in the plane of the disc l4 so as tofacilitate chopping of the beam. The source 22 is so positioned thatwhen the picture modulated beam from the source 9 is incident on thecell I2, through an opening I5 in the chopper, the unmodulated beam fromthe source 22 is cut off. It will be understood that it is within thescope of my invention to use separate light interrupters or shuttersbefore each of the cells I2 and 2I and to arrange for operation of thelight interrupters to produce alternate illumination of the cells fromtheir respective light sources. A chopper or choppers may be dispensedwith if light sources of the glow type illuminated intermit tently areemployed. Such sources if used may conveniently be supplied withalternating currents of a selected frequency and proper phasedisplacement to secure alternate illumination of the photocells.

The interconnected terminals of the photocells are connected to theprimary of a transformer 26, the connection between the cathodes and thetransformer primary including a source of potential illustrated as thebattery 21. It will be understood that the battery 21 may be placed ineither connection to the primary provided that the negative terminal ofthe battery is in communication with the cathodes of the photocells. Thetransformer 26 is preferably of special design a relatively large numberof turns, and it is to be noted that the entire primary is utilized.

e combined output of the photocells is impressed on the amplifier 28from the secondary of the transformer 26. The amplifier 28 in turn isconnected to communication L over which the signals are to betransmitted to a remote facsimile receiver (not shown) of a suitablekind.

In operation of the arrangement described, the light from the source 9is projected upon the background or lightest area of the positivesubject matter on the drum I5 and with the chopper i i rotating, theintensity of the beam from the source 22 is regulated so that thecombined output of the two cells is substantially constant. As the beamfrom the source 9 traverses the subject matter on the peripheral surfaceof the drum 5, the record as reproduced at the receiver w show darkportions when the darkest portion subject matter to be transmitted isscanned and proportional gradations for different light values of theoriginal.

If a received record is desired having less trast than the original, anadjustment may be with the light from the source 9 incident on thelightest portion, or example, of the scanned field, and the light fromthe source 22 may be adjusted so that any desired amount of alternatingcurrent output is derived from the cells and 2i. In this condition ofthe system, the amount of unbalance as the scanning proceeds isdetermined by the contrast desired. The light value, therefore, of thebackground of the received record can be readily controlled.

The ease of adjustment of the amount of light in either beam affords aready means. of compensating optically for differences in thecharacteristics of the photocells I2 and 2|.

In the modified form of the invention illustrated by Fig. 2 of thedrawing, the light sources the general optical arrangement are similarto that already fully described in connection with Fig. l and likeelements have been given similar reference characters. The photocell 2Iand the light source 22 are arranged with respect to the perforations I5 in the disc I4 in a manner to provide simultaneous illumination of thecells I2 and 25. These cells are connected in a bridge circuit and formtwo arms thereof. The remaining two bridge arms are the primarysections. 30 and 3! of the transformer 32. A battery 33 furnishes theoperating potential for the two photocells and 1131's connected with thecells and the transformer primaries in such a manner that thephotoelectric current from one cell opposes that from the other cellpermitting the cells to. be simultaneously rather than alternatelyilluminated. Light interruption may be accomplished by substituting forthe disc It the means set forth above.

In operation, the beams from the sources 9 and 22 are chopped in phaseand the light from the source'22 is adjusted so that the photoelectriccurrents from the two cells are equal and magnetically opposite whilescanning the lightest portion of the subject matter on the drum 5. Asthe darker portions of the subject matter are scanned, an alternatingcurrent appears in the secondary of the transformer 32. This secondarycurrent for a given portion of the scanned field corresponds in waveform to the wave form of the combined output of the photocells of Fig. 1appearing in the secondary of transformer 26. As stated in connectionwith Fig. 1, the optical arrangement disclosed permits ready adjustmentof the two light beams to compensate for difierences in thecharacteristics of the two cells.

While I have described and explained my invention in detail inconnection with two illustrative embodiments thereof, it is to beunderstood that the invention may be embodied in other forms, and,therefore, the invention is not limited except as indicated by the termsand scope of the appended claim.

I claim:

In a photoelectric pickup arrangement for producing aninversion ofpicture currents, two photoelectric cells each comprisinga plurality ofelectrodes, a light source, means to supply inter mittent light fromsaid source and means for modulating said light in accordance with apositive copy of given subject matter, means for projecting saidintermittent modulated light onto one of said cells, an independentlight source, means to supply intermittent light from said independentsource for illuminating the other of said cells simultaneously withpicture modulated illumination of said first cell, a direct currentsource, means connecting corresponding electrodes of said cells with oneterminal of said source, a transformer having a primary winding providedwith a center tap connected to the remaining terminal of said source,and means connecting the terminals of said primary winding with othercorresponding electrodes of said cells whereby the output of said cellsis combined in said primary 180 out of phase to effect an inversion ofpicture currents.

' RALEIGH J. WISE.

